FEATURES

APPLICATIONS

DESCRIPTION/ORDERING INFORMATION

1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR

• Fixed 3.3-V, 5-V, 12-V, and 15-V Options With±5% Regulation (Max) Over Line, Load, andTemperature Conditions

• Adjustable Option With a Range of 1.23 V to37 V and ±4% Regulation (Max) Over Line,Load, and Temperature Conditions

• Specified 1-A Output Current• Wide Input Voltage Range…4.75 V to 40 V• Requires Only Four External Components

(Fixed Versions) and Uses Readily AvailableStandard Inductors

• 52-kHz (Typ) Fixed-Frequency InternalOscillator

• TTL Shutdown Capability With 50-µA (Typ)Standby Current

• High Efficiency…as High as 88% (Typ)• Thermal Shutdown and Current-Limit

Protection With Cycle-by-Cycle CurrentLimiting

• Simple High-Efficiency Step-Down (Buck)Regulator

• Pre-Regulator for Linear Regulators• On-Card Switching Regulators• Positive-to-Negative Converter (Buck-Boost)

The LM2575 greatly simplifies the design of switching power supplies by conveniently providing all the activefunctions needed for a step-down (buck) switching regulator in an integrated circuit. Accepting a wide inputvoltage range and available in fixed output voltages of 3.3 V, 5 V, 12 V, 15 V, or an adjustable output version,the LM2575 has an integrated switch capable of delivering 1 A of load current, with excellent line and loadregulation. The device also offers internal frequency compensation, a fixed-frequency oscillator, cycle-by-cyclecurrent limiting, and thermal shutdown. In addition, a manual shutdown is available via an external ON/OFF pin.

The LM2575 represents a superior alternative to popular three-terminal linear regulators. Due to its highefficiency, it significantly reduces the size of the heat sink and, in many cases, no heat sink is required.Optimized for use with standard series of inductors available from several different manufacturers, the LM2575greatly simplifies the design of switch-mode power supplies by requiring a minimal addition of only four to sixexternal components for operation.

The LM2575 is characterized for operation over the virtual junction temperature range of 0 °C to 85 °C.

LM2575

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Straight Leads5–Lead TO-220 (T)

Top ViewLM2575T-XX

TO-263(S)5-Lead Surface-Mount Package

Top View

Side ViewLM2575S-XX

InternalRegulator

On/Off

_+

_+

1.23-VBand-GapReference

52-kHzOscillator Reset

ThermalShutdown

CurrentLimit

FEEDBACK

4

CIN+

VIN

1Unregulated

DC Input

GND

3

OUTPUT

2

ON/OFF

5

COUT

+D1

LOAD

VOUT

1-ASwitchDriver

Fixed-GainError Amp

Comparator

R2

R11 k

3.3 V: R2 = 1.7 k5 V: R2 = 3.1 k12 V: R2 = 8.84 k15 V: R2 = 11.3 kADJ: R1 = Open, R2 = 0 Ω

L1

LM2575-057-V to 40-VUnregulated

DC Input

CIN100 µF

+

+VIN

1

3 GND 5 ON/OFF

D11N5819

OUTPUT2

L1

330 µH

COUT330 µF

+

FEEDBACK4

5-VRegulatedOutput 1-A Load

L2

20 µH

C1100 µF

+

Optional Output Ripple Filter

FUNCTIONAL BLOCK DIAGRAM

A. Pin numbers are for the KTT (TO-263) package.

A. Pin numbers are for the KTT (TO-263) package.

Figure 1. Typical Application Circuit (Fixed Version)

LM2575

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Absolute Maximum Ratings (1)

Package Thermal Data (1)

Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)

MIN MAX UNIT

VIN Supply voltage 42 V

ON/OFF pin input voltage –0.3 VIN V

Output voltage to GND (steady state) –1 V

TJ Maximum junction temperature 150 °C

Tstg Storage temperature range –65 150 °C

(1) Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratingsonly, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operatingconditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

PACKAGE BOARD θJC θJCB θJA

PDIP (N) High K, JESD 51-7 51°C/W 67°C/W

TO-263 (KTT) High K, JESD 51-5 TBD TBD

(1) Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambienttemperature is PD = (TJ(max) – TA)/θJA. Operating at the absolute maximum TJ of 150°C can affect reliability.

over operating free-air temperature range (unless otherwise noted)

MIN MAX UNIT

VIN Supply voltage 4.75 40 V

TJ Operating virtual junction temperature 0 85 °C

LM2575

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Electrical CharacteristicsILOAD = 200 mA, VIN = 12 V for 3.3-V, 5-V, and adjustable versions, VIN = 25 V for 12-V version, VIN = 30 V for 15-V version(unless otherwise noted) (see Figure 2)

PARAMETER TEST CONDITIONS TJ MIN TYP MAX UNIT

VIN = 12 V, ILOAD = 0.2 A 25°C 3.234 3.3 3.366

LM2575-33 25°C 3.168 3.3 3.4324.75 V ≤ VIN ≤ 40 V,0.2 A ≤ ILOAD ≤ 1 A Full range 3.135 3.465

VIN = 12 V, ILOAD = 0.2 A 25°C 4.9 5 5.1

LM2575-05 25°C 4.8 5 5.28 V ≤ VIN ≤ 40 V,0.2 A ≤ ILOAD ≤ 1 A Full range 4.75 5.25

VOUT Output voltage VVIN = 25 V, ILOAD = 0.2 A 25°C 11.76 12 12.24

LM2575-12 25°C 11.52 12 12.4815 V ≤ VIN ≤ 40 V,0.2 A ≤ ILOAD ≤ 1 A Full range 11.4 12.6

VIN = 30 V, ILOAD = 0.2 A 25°C 14.7 15 15.3

LM2575-15 25°C 14.4 15 15.618 V ≤ VIN ≤ 40 V,0.2 A ≤ ILOAD ≤ 1 A Full range 14.25 15 15.75

VIN = 12 V, VOUT = 5 V, 25°C 1.217 1.23 1.243ILOAD = 0.2 AFeedback voltage LM2575-ADJ V25°C 1.193 1.23 1.2678 V ≤ VIN ≤ 40 V, VOUT = 5 V,

0.2 A ≤ ILOAD ≤ 1 A Full range 1.18 1.28

LM2575-33 VIN = 12 V, ILOAD = 1 A 75

LM2575-05 VIN = 12 V, ILOAD = 1 A 77

LM2575-12 VIN = 15 V, ILOAD = 1 A 88η Efficiency 25°C %LM2575-15 VIN = 18 V, ILOAD = 1 A 88

VIN = 12 V, VOUT = 5 V,LM2575-ADJ 77ILOAD = 1 A

25°C 50 100IIB Feedback bias current VOUT = 5 V (ADJ version only) nA

Full range 500

25°C 47 52 58fo Oscillator frequency (1) kHz

Full range 42 63

25°C 0.9 1.2VSAT Saturation voltage IOUT = 1 A (2) V

Full range 1.4

Maximum duty cycle (3) 25°C 93 98 %

25°C 1.7 2.8 3.6ICL Peak current (1) (2) A

Full range 1.3 4

VIN = 40 (4), Output = 0 V 2IL Output leakage current 25°C mA

VIN = 40 (4), Output = –1 V 7.5 30

IQ Quiescent current (4) 25°C 5 10 mA

ISTBY Standby quiescent current OFF (ON/OFF pin = 5 V) 25°C 50 200 µA

25°C 2.2 1.4VIH OFF (VOUT = 0 V)

Full range 2.4ON/OFF logic input level V

25°C 1.2 1VIL ON (VOUT = nominal voltage)

Full range 0.8

IIH OFF (ON/OFF pin = 5 V) 12 30ON/OFF input current 25°C µA

IIL OFF (ON/OFF pin = 0 V) 0 10

(1) In the event of an output short or an overload condition, self-protection features lower the oscillator frequency to ∼18 kHz and theminimum duty cycle from 5% to ∼2%. The resulting output voltage drops to ∼40% of its nominal value, causing the average powerdissipated by the IC to lower.

(2) Output is not connected to diode, inductor, or capacitor. Output is sourcing current.(3) Feedback is disconnected from output and connected to 0 V.(4) To force the output transistor off, FEEDBACK is disconnected from output and connected to 12 V for the adjustable, 3.3-V, and 5-V

versions; and 25 V for the 12-V and 15-V versions.

LM2575

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APPLICATION INFORMATION

Layout Guidelines

LM2575-xxFixed Output

CIN100 µF

+

+VIN

1

3 GND 5 D1

2

L1

330 µH

COUT330 µF

+

4

LOAD

VOUT

VINUnregulated

DC Input

CIN = 100 µF, Aluminum ElectrolyticCOUT = 330 µF, Aluminum ElectrolyticD1 = SchottkyL1 = 330 µH

Fixed Output Voltage Versions

LM2575(ADJ)

CIN100 µF

+

+VIN

1

3 GND 5 ON/OFF D111DQ06

OUTPUT

2

L1

330 µH

COUT330 µF

+

FEEDBACK4

LOAD

VOUT

7-V to 60-VUnregulated

DC Input

Adjustable Output Voltage Versions

VOUT = VREF(1 + R2/R1) = 5 V

Where, VREF = 1.23 VR1 = 2 kR2 = 6.12 k

R2

R1

ON/OFF

OUTPUT

FEEDBACK

With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasiticinductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result inunwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated byheavy lines should be minimized. Optimal results can be achieved by single-point grounding (see Figure 2) or byground-plane construction. For the same reasons, the two programming resistors used in the adjustable versionshould be located as close as possible to the regulator to keep the sensitive feedback wiring short.

A. Pin numbers are for the KTT (TO-263) package.

Figure 2. Test Circuit and Layout Guidelines

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Input Capacitor (CIN)

IC,RMS 1.2(ton

T) ILOAD, where:

ton

T

VOUT

VINbuck regulator, and

ton

T

|VOUT|(|VOUT|VIN) buck−boost regulator

Output Capacitor (COUT)

Catch Diode

Inductor

APPLICATION INFORMATION (continued)

For stability concerns, an input bypass capacitor (electrolytic, CIN ≥ 47 µF) needs to be located as close aspossible to the regulator. For operating temperatures below –25°C, CIN may need to be larger in value. Inaddition, since most electrolytic capacitors have decreasing capacitances and increasing ESR as temperaturedrops, adding a ceramic or solid tantalum capacitor in parallel increases the stability in cold temperatures.

To extend the capacitor operating lifetime, the capacitor RMS ripple current rating should be:

For both loop stability and filtering of ripple voltage, an output capacitor also is required, again in close proximityto the regulator. For best performance, low-ESR aluminum electrolytics are recommended, although standardaluminum electrolytics may be adequate for some applications. Based on the following equation:

Output Ripple Voltage = (ESR of COUT) × (inductor ripple current)

Output ripple of 50 mV to 150 mV typically can be achieved with capacitor values of 220 µF to 680 µF. LargerCOUT can reduce the ripple 20 mV to 50 mV peak-to-peak. To improve further on output ripple, paralleling ofstandard electrolytic capacitors may be used. Alternatively, higher-grade capacitors such as “high frequency”,“low inductance”, or “low ESR” can be used.

The following should be taken into account when selecting COUT:• At cold temperatures, the ESR of the electrolytic capacitors can rise dramatically (typically 3× nominal value

at –25°C). Because solid tantalum capacitors have significantly better ESR specifications at coldtemperatures, they should be used at operating temperature lower than –25°C. As an alternative, tantalumsalso can be paralleled to aluminum electrolytics and should contribute 10% to 20% to the total capacitance.

• Low ESR for COUT is desirable for low output ripple. However, the ESR should be greater than 0.05 Ω toavoid the possibility of regulator instability. Hence, a sole tantalum capacitor used for COUT is mostsusceptible to this occurrence.

• The capacitor’s ripple current rating of 52 kHz should be at least 50% higher than the peak-to-peak inductorripple current.

As with other external components, the catch diode should be placed close to the output to minimize unwantednoise. Schottky diodes have fast switching speeds and low forward voltage drops and, thus, offer the bestperformance, especially for switching regulators with low output voltages (VOUT < 5 V). If a high-efficiency,fast-recovery, or ultra-fast-recovery diode is used in place of a Schottky, it should have a soft recovery (versusabrupt turn-off characteristics) to avoid the chance of causing instability and EMI. Standard 50-/60-Hz diodes,such as the 1N4001 or 1N5400 series, are NOT suitable.

Proper inductor selection is key to the performance-switching power-supply designs. One important factor toconsider is whether the regulator will be used in continuous (inductor current flows continuously and never dropsto zero) or in discontinuous mode (inductor current goes to zero during the normal switching cycle). Each modehas distinctively different operating characteristics and, therefore, can affect the regulator performance andrequirements. In many applications, the continuous mode is the preferred mode of operation, since it offersgreater output power with lower peak currents, and also can result in lower output ripple voltage. The advantagesof continuous mode of operation come at the expense of a larger inductor required to keep inductor currentcontinuous, especially at low output currents and/or high input voltages.

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Output Voltage Ripple and Transients

Feedback Connection

ON/OFF Input

Grounding

APPLICATION INFORMATION (continued)

The LM2575 can operate in either continuous or discontinuous mode. With heavy load currents, the inductorcurrent flows continuously and the regulator operates in continuous mode. Under light load, the inductor fullydischarges and the regulator is forced into the discontinuous mode of operation. For light loads (approximately200 mA or less), this discontinuous mode of operation is perfectly acceptable and may be desirable solely tokeep the inductor value and size small. Any buck regulator eventually will operate in discontinuous mode whenthe load current is light enough.

The type of inductor chosen can have advantages and disadvantages. If high performance/quality is a concern,then more-expensive toroid core inductors are the best choice, as the magnetic flux is contained completelywithin the core, resulting in less EMI and noise in nearby sensitive circuits. Inexpensive bobbin core inductors,however, generate more EMI as the open core will not confine the flux within the core. Multiple switchingregulators located in proximity to each other are particularly susceptible to mutual coupling of magnetic fluxesfrom each other’s open cores. In these situations, closed magnetic structures (such as a toroid, pot core, orE-core) are more appropriate.

Regardless of the type and value of inductor used, the inductor never should carry more than its rated current.Doing so may cause the inductor to saturate, in which case the inductance quickly drops, and the inductor lookslike a low-value resistor (from the dc resistance of the windings). As a result, switching current rises dramatically(until limited by the current-by-current limiting feature of the LM2575) and can result in overheating of theinductor and the IC itself. Note that different types of inductors have different saturation characteristics.

As with any switching power supply, the output of the LM2575 will have a sawtooth ripple voltage at the switchingfrequency. Typically about 1% of the output voltage, this ripple is due mainly to the inductor sawtooth ripplecurrent and the ESR of the output capacitor (see note on COUT). Furthermore, the output also may contain smallvoltage spikes at the peaks of the sawtooth waveform. This is due to the fast switching of the output switch andthe parasitic inductance of COUT. These voltage spikes can be minimized through the use of low-inductancecapacitors.

There are several ways to reduce the output ripple voltage: a larger inductor, a larger COUT, or both. Anothermethod is to use a small LC filter (20 µH and 100 µF) at the output. This filter can reduce the output ripplevoltage by a factor of 10 (see Figure 2).

For fixed voltage options, FEEDBACK must be wired to VOUT. For the adjustable version, FEEDBACK must beconnected between the two programming resistors. Again, both of these resistors should be in close proximity tothe regulator, and each should be less than 100 kΩ to minimize noise pickup.

ON/OFF should be grounded or be a low-level TTL voltage (typically <1.6 V) for normal operation. To shut downthe LM2575 and put it in standby mode, a high-level TTL or CMOS voltage should be supplied to this pin.ON/OFF should not be left open and safely can be pulled up to VIN with or without a pullup resistor.

The power and ground connections of the LM2575 must be low impedance to help maintain output stability. Forthe 5-pin packages, both pin 3 and tab are ground, and either connection can be used as they are both part ofthe same lead frame. With the 16-pin and 24-pin packages, all the ground pins (including signal and powergrounds) should be soldered directly to wide PCB copper traces to ensure low-inductance connections and goodthermal dissipation.

LM2575

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LM2575

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Important statement:

Huaguan Semiconductor Co,Ltd. reserves the right to changethe products and services provided without notice. Customersshould obtain the latest relevant information before ordering,and verify the timeliness and accuracy of this information.

Customers are responsible for complying with safetystandards and taking safety measures when using ourproducts for system design and machine manufacturing toavoid potential risks that may result in personal injury orproperty damage.

Our products are not licensed for applications in life support,military, aerospace, etc., so we do not bear the consequencesof the application of these products in these fields.

Our documentation is only permitted to be copied withoutany tampering with the content, so we do not accept anyresponsibility or liability for the altered documents.